A bearing device for vehicle wheel that supports a vehicle wheel rotatable is conventionally known (see, for example, Patent Literature 1). In such a bearing device for vehicle wheel, an outer member is fixed to a vehicle body. Further, an inner member is disposed inside the outer member, and a plurality of rolling elements are interposed between their respective rolling surfaces of the outer member and the inner member. As described above, the bearing device for vehicle wheel constitutes a rolling bearing structure that makes the vehicle wheel attached to the inner member rotatable.
Meanwhile, in such a bearing device for vehicle wheel, so-called undercut work is applied to a portion where an inner rolling surface formed on an inner side of the inner member and an inner-side flange surface of the inner rolling surface intersect (hereinafter, referred to as “inner-side undercut part” (see FIG. 9)). Further, so-called undercut work is applied to a portion where an inner rolling surface formed on an outer side of the inner member and an outer-side flange surface of the inner rolling surface intersect (hereinafter, referred to as “outer-side undercut part” (see FIG. 9)). The inner-side undercut part and the outer-side undercut part are recesses formed to allow a cutting edge of a cutting tool to move through.
Furthermore, in such a bearing device for vehicle wheel, a vehicle wheel installation flange is provided adjacent to the inner rolling surface formed on the outer side of the inner member. Therefore, when a large and impulsive external force is applied to the vehicle wheel installation flange due to that, for example, the vehicle wheel runs on a curb, stress may concentrate on the outer-side undercut part near a base end portion of the vehicle wheel installation flange (see a mark X shown in FIG. 9). Thus, there has been proposed a bearing device for vehicle wheel that secures the function of the outer-side flange surface by fitting another member without forming the outer-side flange surface on the outer side of the inner member (see, for example, Patent Literature 2). Such a bearing device for vehicle wheel, however, has a problem in that cutting work takes a longer time, a large number of parts are required, and a structure becomes complicated. From such circumstances, there has been a demand for a bearing device for vehicle wheel that can reduce a value of stress produced in the outer-side undercut part even with a simple structure. Accordingly, there has been a demand for a bearing device for vehicle wheel that can secure high rigidity even with a simple structure.